The present invention relates to methods for determining a reference energy profile, to a device for forming a battery, to a method for forming a battery, to a usage of a reference energy profile and to a computer program. Additionally, the present invention relates to a method for an improved formation of galvanic cells or electrical battery cells which form a solid electrolyte interface (SEI), and to an optimized method for guiding a formation current.
Formation is a manufacturing step when producing galvanic cells or electrical battery cells. Formation refers to the first charge and discharge processes where the so-called SEI forms. This process is used for activating the electrochemical processes and/or characteristics of the battery cell. Forming the SEI has a decisive role for important cell characteristics, like internal resistance and cycle stability. A stable uniform layer is of advantage here. Up to now, formation (i.e. charging and discharging) has been realized using very low electrical currents. This in turn results in a time-consuming and, consequently, expensive manufacturing step which may restrict the throughput of the production chain.
Methods known today rely on constant low currents which are to allow a slow uniform SEI formation. A fixed electrical current up to the respective final voltage is set per charge and discharge process. In publications [1] and [2], increasing the current starting from a predefined voltage threshold is suggested, wherein a constant current is applied between the one to three steps. Initially, the smallest possible current intensity (mostly 1/20 C, 1/15 C or 1/10 C) is set, which is based on experience values. With further developed methods, starting from a voltage threshold, the current is increased or formation terminated already, since experiments have shown that after that less SEI is formed and the termination has tolerable negative effects on the cycle stability. Such a procedure is described in [3], for example. A partial acceleration of the method is achieved here by tolerating a slight deterioration of SEI homogeneity or SEI thickness.
FIG. 11 shows a schematic illustration of a concept 90 for forming a battery cell 92 in accordance with the known technology. The battery cell 92 is connected electrically to a direct current source 96 via contactings 94a and 94b. Formation here is done using a constant current I. As is described in [1] and [2], the current I can be controlled by means of a controller 98 such that it is increased in a few predefined steps, wherein a constant current value is set between the steps.
US 2015/0060290 A1 describes a concept where a small current intensity is used up to a predefined point and, after that, a higher, second current intensity is switched to.
DE 3736069 A1 describes applying a regulated current for forming lead-acid batteries. However, when compared to forming galvanic cells, a different electrochemical target is aimed at here. When forming lead-acid batteries, an active layer is set up. Setting up an SEI includes forming an electrically insulating layer between active particles (electrode) and the electrolyte. The electrochemical processes are not comparable.
Consequently, what would be desirable is a concept for forming a battery which, when compared to known methods, allows implementing an improved formation of batteries in a short time and/or obtaining an SEI of high homogeneity.
Consequently, an object underlying the present invention is providing a concept which allows forming a battery in a short time and/or at high an SEI homogeneity.